Computers include general purpose central processing units (CPUs) or “processors” that are designed to execute a specific set of system instructions. A group of processors that have similar architecture or design specifications may be considered to be members of the same processor family. Examples of current processor families include the Motorola 680×0 processor family, manufactured by Motorola, Inc. of Phoenix, Ariz.; the Intel 80×86 processor family, manufactured by Intel Corporation of Sunnyvale, Calif.; and the PowerPC processor family, which is manufactured by Motorola, Inc. and used in computers manufactured by Apple Computer, Inc. of Cupertino, Calif. Although a group of processors may be in the same family because of their similar architecture and design considerations, processors may vary widely within a family according to their clock speed and other performance parameters.
Each family of microprocessors executes instructions that are unique to the processor family. The collective set of instructions that a processor or family of processors can execute is known as the processor's instruction set. As an example, the instruction set used by the Intel 80×86 processor family is incompatible with the instruction set used by the PowerPC processor family. The Intel 80×86 instruction set is based on the Complex Instruction Set Computer (CISC) format. The Motorola PowerPC instruction set is based on the Reduced Instruction Set Computer (RISC) format. CISC processors use a large number of instructions, some of which can perform rather complicated functions, but which require generally many clock cycles to execute. RISC processors use a smaller number of available instructions to perform a simpler set of functions that are executed at a much higher rate.
The uniqueness of the processor family among computer systems also typically results in incompatibility among the other elements of hardware architecture of the computer systems. A computer system manufactured with a processor from the Intel 80×86 processor family will have a hardware architecture that is different from the hardware architecture of a computer system manufactured with a processor from the PowerPC processor family. Because of the uniqueness of the processor instruction set and a computer system's hardware architecture, application software programs are typically written to run on a particular computer system running a particular operating system.
Virtual Machines
Computer manufacturers want to maximize their market share by having more rather than fewer applications run on the microprocessor family associated with the computer manufacturers' product line. To expand the number of operating systems and application programs that can run on a computer system, a field of technology has developed in which a given computer having one type of CPU, called a host, will include a virtualizer program that allows the host computer to emulate the instructions of an unrelated type of CPU, called a guest. Thus, the host computer will execute an application that will cause one or more host instructions to be called in response to a given guest instruction, and in this way the host computer can both run software designed for its own hardware architecture and software written for computers having an unrelated hardware architecture.
As a more specific example, a computer system manufactured by Apple Computer, for example, may run operating systems and program written for PC-based computer systems. It may also be possible to use virtualizer programs to execute concurrently on a single CPU multiple incompatible operating systems. In this latter arrangement, although each operating system is incompatible with the other, virtualizer programs can host each of the several operating systems and thereby allowing the otherwise incompatible operating systems to run concurrently on the same host computer system.
When a guest computer system is emulated on a host computer system, the guest computer system is said to be a “virtual machine” as the guest computer system only exists in the host computer system as a pure software representation of the operation of one specific hardware architecture. The terms virtualizer, emulator, direct-executor, virtual machine, and processor emulation are sometimes used interchangeably to denote the ability to mimic or emulate the hardware architecture of an entire computer system using one or several approaches known and appreciated by those of skill in the art. Moreover, all uses of the term “emulation” in any form is intended to convey this broad meaning and is not intended to distinguish between instruction execution concepts of emulation versus direct-execution of operating system instructions in the virtual machine. Thus, for example, the Virtual PC software created by Connectix Corporation of San Mateo, Calif. “emulates” (by instruction execution emulation and/or direct execution) an entire computer that includes an Intel 80×86 Pentium processor and various motherboard components and cards, and the operation of these components is “emulated” in the virtual machine that is being run on the host machine. A virtualizer program executing on the operating system software and hardware architecture of the host computer, such as a computer system having a PowerPC processor, mimics the operation of the entire guest computer system.
The virtualizer program acts as the interchange between the hardware architecture of the host machine and the instructions transmitted by the software (e.g., operating systems, applications, etc.) running within the emulated environment. This virtualizer program may be a host operating system (HOS), which is an operating system running directly on the physical computer hardware (and which may comprise a hypervisor, discussed in greater detailed later herein). Alternately, the emulated environment might also be a virtual machine monitor (VMM) which is a software layer that runs directly above the hardware, perhaps running side-by-side and working in conjunction with the host operating system, and which can virtualize all the resources of the host machine (as well as certain virtual resources) by exposing interfaces that are the same as the hardware the VMM is virtualizing. This virtualization enables the virtualizer (as well as the host computer system itself) to go unnoticed by operating system layers running above it.
To summarize, processor emulation enables a guest operating system to execute on a virtual machine created by a virtualizer running on a host computer system, said host computer system comprising both physical hardware and a host operating system.
Processor and Memory Topology
Modern operating system schedulers take into account the processor and memory topology of the machine to maximize performance. This is usually done at startup and, for an operating system executing on physical hardware, this is usually sufficient because the processor topology of physical hardware remains constant. The Windows Operating System (Windows XP, Windows 2003) and other operating systems typically determine the topology of the system at boot time in two ways: (a) by examining the memory and processor node topology information in the BIOS Static Resource Affinity Table (SRAT) and (b) by reading self-contained processor identification data (CPUID in x86/x64 processors) to determine specific Simultaneous Multithreading (SMT, a.k.a. hyperthreading) and multicore topologies.
As used herein, the term “processor topology” is broadly intended to refer to physical characteristics of the processor and associated memory that, if known by an operating system, could theoretically enable an operating system to better utilize the associated processor resources. Processor topology may include, but is not limited to, the following: static processor information such as SMT, multicore, and BIOS' SRAT data and/or information; static NUMA information such as processor, memory, and I/O resource arrangements; and any changes to the foregoing.
In a virtual machine environment, however, while the physical processor topology for the “hosting agent” (the host operating system, virtual machine monitor, and/or hypervisor) remains constant, the physical resources assigned to a virtualizer, and thus the virtual machine, may vary rapidly over time, making the topology assumptions made by the guest operating system running on the virtual machine inaccurate and hence inefficient.
While the dynamic nature of the topology can be mitigated by always using the same physical processor assignments for virtual processors or by limiting the assignments to a specific node, this would severely and negatively impact the virtualizer's ability to make optimal use of all host resources. Therefore, what is needed in the art is means for rectifying the inefficiency of a changing virtual topology without negatively impacting the virtualizers ability to make optimal use of all host resources.